My rails are stamped with 28D. These are heavy Dual Pane windows. Your product that appears to match is Product Code: S380-29
But you don't list Letters for the weight code.
Which of these is the 28D replacement?
Tom from SWISCO responded:
March 2, 2017
Thanks for posting. A stamp of 28D usually corresponds to our 2840 option, but you can always weigh your sash on a scale to confirm.